1. Field of the Invention
The present invention relates to a motor control apparatus that improves the starting process of a synchronous motor used to drive a compressor of an air conditioner or the like.
2. Description of the Related Art
Disclosed in JP-A-2001-54295 is a sensorless motor control apparatus that comprises means for detecting electric current flowing through coils of a synchronous motor, means for detecting the phase difference between current and voltage supplied to the coils, and means for detecting completion of starting of the synchronous motor based on the phase difference. In this control apparatus, the phase difference between current and voltage after the start of the synchronous motor is detected, and the detection is repeated while changing the voltage and frequency of electric power supplied to the coils, if a variation in the detected phase differences is larger than a predetermined value. When the variation in phase difference is reduced to be within a predetermined range, it is determined that the starting is completed.
However, this motor control apparatus entails a drawback that much time is required to determine the completion of starting since the determination must be repeated as long as a variation in the detected phase differences is larger than the predetermined value, and entails a drawback that an arithmetic unit is required to have high processing ability since it has to perform the complicated determination processing.